The invention relates to a fluid operated rotary drive comprising a hose body extending between two head pieces, and a power transmitting structure engaged with the two head pieces and adapted for cooperation with said hose body, said power transmitting structure being adapted to cause a relative rotary movement between the two head pieces when the interior space of the hose body is acted upon by fluid.
Known fluid operated rotary drives, as are more particularly employed in pneumatic systems, possess a rigid housing for example, in which a piston is arranged for axial motion, said piston so cooperating with the housing via further means that in the course of the axial motion it simultaneously performs a rotary movement. This rotary movement is transmitted with the aid of a rod, which is drivingly connected with the piston in such a manner as to prevent relative rotation so that the rod serves to make the rotary movement available, which for example can be utilized for the operation of a valve. A rotary drive of this type is disclosed in the German patent publication 4,427,779 C2.
A disadvantage in connection with such rotary drives is the high degree of mechanical complexity involved in their manufacture, be it in connection with the guidance of the piston or with the seal between it and the housing. These known rotary drives are consequently relatively expensive and liable to wear.
Therefore in the U.S. Pat. No. 3,638,536 a proposal has already been made for a fluid operated rotary drive of the type initially mentioned, in the case of which the rotary motion is produced by a hose body extending axially between two head pieces and provided with an integrated power transmitting structure. The hose body is here designed in the form of a contracting hose, which under the action of internal pressure expands radially and simultaneously via the power transmitting structure pulls the two head pieces toward each other. Owing to the design of the power transmitting structure as a strand structure with mutually parallel, helically extending ties, the axial contraction simultaneously results in a relative rotary movement between the two head pieces, and such rotary movement may be employed for the actuation of an object to be turned. However, the angular movement of the drive provided is relatively small so that the field of application of this known rotary drive has strict limitations and practical use is questionable.
Accordingly one object of the present invention is to provide a fluid operated rotary drive of the type initially mentioned ensuring larger angles of rotation while having compact dimensions.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention the two head pieces bear against each other via support means while permitting their relative motion in such a manner that they are held against performing an axial relative motion toward and/or away from one another in order to maintain their relative axial position.
It has been found that if the relative ax al position of the two head pieces is set while simultaneously permitting a degree of freedom about the longitudinal axis, substantially larger angles of rotation are possible than is the case with a hose body designed in the form of a contraction element. Maintenance of the relative axial position is ensured by a supporting means effective between the two head pieces, whose axial direction of action may be selected in manner dependent on the design of the power transmission structure. It has been found that, dependent on the form of the power transmission structure and taking into account the axially acting working pressure areas of the head pieces, there is a certain tendency of the head pieces to move apart or to move together. This tendency to move out of position can be countered by suitable design of the support means. It is convenient then to select a form of the support means, which prevents axial relative movement between the two head pieces in both axial directions. The invention renders possible the production of rotary movements and torques with a predetermined coordination between working pressure, angular displacement and torque while avoiding axial movements as further dependent variables.
Further advantageous developments of the invention are defined in the claims.
In order to ensure reliable operation of the rotary drive even when it is not purely axial forces which are acting on the head pieces, it is an advantage to design the support means in such a manner that it is able to take up transverse forces and/or bending moments occurring between the two head pieces. Although for compensation of these loads it would also be possible to have resort to external means, as for example the objects themselves which are to be turned in relation to one another (if such objects are suitably mounted for rotation) to render possible universal application of the rotary drive, it is however best to integrate these support functions as well in the support means itself.
Moreover it is also to be noted that the support means does not necessarily have to be designed as a direct component of the rotary drive. Its function may, given a suitable design, be performed by the objects themselves to be turned in relation to one another or by other suitable external means.
The power or force transmission structure is preferably designed in the form of a strand structure, which possesses a plurality of flexibly bending ties extending between the head pieces and which more particularly extend with the form of a helical screw means between the two head pieces and which are responsible for the relative rotary movement when the hose body is acted upon internally. It would be feasible as well to set the relative position of the ties using warp-like transverse strands or with some other type of crosslinking means. However it has turned out to be particularly advantageous to design the strand structure exclusively in the form of ties running alongside each other and with the same longitudinal alignment. The position thereof is conveniently stabilized by having them at least partly embedded in the hose body, for example by vulcanization.
It has been found that by using a cylindrical strand- or thread-reinforced elastomeric hose only coiled in one direction, whose ends are locked on head pieces, said head pieces for their part being locked in the axial direction while being able to run freely in relation to the longitudinal axis of the hose, different degrees of rotation and levels of torque accurately correspond to different internal pressures and volumes of the hose.
It has been found that in the case of an initial oblique setting of the ties, that is to say in the pressureless state of the hose body, of more than 54.7xc2x0 in relation to the longitudinal direction of the hose body when under pressure, there is at least initially a tendency of the head pieces to move apart axially. In this case a supporting means is employed, which at least prevents this relative axial movement. On the other hand in the case of an initial oblique setting of the ties of less than 54.7xc2x0 and with the hose body under pressure there is an at least initial tendency to contract so that in such a case the supporting means should be so designed that the supporting means at least prevents a relative axial movement of the two head pieces in the form of their moving toward one another. Since during operation of the rotary drive the oblique angle will be reduced with an increase in twist it is to be recommended to have an axial support, effective between the two head pieces, when the initial oblique setting is equal to more than 54.4xc2x0 and in the course of operation becomes less than this value.
It is has been found to be particularly advantageous to design the strand structure in such a manner that the initial oblique setting, measured in relation to the longitudinal direction of the hose body, of the ties is in a range between 55xc2x0 and 65xc2x0.
In principle it would be feasible to install the supporting means at least partly outside hose body. However it is substantially more advantageous, owing to the saving in space, to accommodate the supporting means in the interior space of the hose body. This furthermore results in an effect reducing the amount of fluid, because the volume to be filled with fluid in the interior space of the hose body is reduced.
In order to provide particularly large angles of rotation between the two head pieces the hose body including contraction structure is designed with a correspondingly large overall length. However without additional measures this does lead to an excessively great radial extent of the hose body. For this reason in the case of rotary drives with relatively long hose bodies it is preferable to provide the respective hose body with means which locally influence the radial expansion of the hose body on the application of internal pressure and more particularly prevent same and here are referred to as constraining means. These constraining means can be distributed along the entire length of the hose body, it being for example a question of individual elements, which are more particularly designed in the form of rings or belts and are arranged coaxially in relation to the hose body with an axial spacing between them. In this respect it can be a question of rigid ring elements of plastic material or of metal. It would also be feasible to provide a fiber-like design of tough flexible material, as for example textile material.
In the case of a further convenient embodiment of the invention the constraining means are constituted by at least one helical body arranged coaxially in relation to the hose body, such helical body extending with the same or opposite hand as the strand structure along the periphery of the hose body, its configuration being selected to be similar to a helical spring for example.
The constraining means may be placed on the outer periphery of the hose body, although it is preferred for same to be at least partially and more especially completely integrated in the hose body.
In order to provide for a predetermined angle of turning it is furthermore convenient to have means which limit radial deformation of the hose body. They may be arranged in the interior space of the hose body or outside it and preferably will perform an abutment function.
Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of one embodiment thereof in conjunction with the accompanying drawings.